#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define endl '\n'
const int N = 2e5 + 5;

int n, m, d, l;
int a[N];

void solve() {
  cin >> n >> d >> m >> l;
  rep(i, 1, n) {
    ll x = (i - 1ll) * m + l;
    ll k = x / d;
    ll y = k * d + d;
    ll z = i == n ? 1e18 : 1ll * i * m;
    if (y < z) {
      cout << y;
      return;
    }
  }
  return;
}
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int t;
  t = 1;
  while (t--) solve();
  return 0;
}